1. Field of the Invention
The present invention relates to the field of data transmission control, and more particularly, to a connection management method in which the user is informed of a change in connection management status between devices connected by a digital interface, and a command structure therefor.
2. Description of the Related Art
Household or industrial equipment can be interconnected by a bus of a predetermined digital interface format such as the Institute of Electrical and Electronics Engineers, Inc., (IEEE) 1394 to transmit or receive real-time data to or from each other. For example, when a digital television (DTV), digital video camcorder, a set-top box (STB), and the like are interconnected via the IEEE 1394 to form a network, real time data such as video and audio information is transmitted between these devices.
As shown in FIG. 1 illustrating a general network system connected via the IEEE 1394, real time data is output from a virtual output plug of a first device and input to an input plug of a second device. In this case, the connection is made conceptually rather than physically. A source device (herein STB 100) includes an output plug 101 for transmitting information and an output plug control register (oPCR) 111 for controlling the flow of information output through the output plug 101. A sink device (herein DTV 200) includes an input plug 201 for receiving information and an input plug control register (iPCR) 211 for controlling the flow of information input to the input plug 201. A control device having a controller 300 can be one of the STB 100 and the DTV 200, or another third-party device, and serves to establish a connection so that a control value of the oPCR 111 and the iPCR 211 can be controlled to transmit data, or terminate the connection.
Accordingly, real time data is transmitted from the output plug 101 to the input plug 201. In this case, the related control information is written in the oPCR 111 and the iPCR 211 corresponding to the output and input plugs 101 and 201, respestively, and the controller 300 reads a value written in the oPCR 111 and the iPCR 211 or writes a control value therein to control the flow of real time data.
The control value to be written in the oPCR 111 and the iPCR 211 will be described with reference to FIGS. 2 and 3. The format of the 32-bit oPCR 111 shown in FIG. 2 is described as follows. The numbers below each region denote the number of allotted bits. An on-line region indicates whether a corresponding output plug is on-line (“1” value) or off-line (“0” value). A broadcast connection counter region indicates whether a broadcast-out connection exists (“1” value) or not (“0” value) in the output plug, whereas a point-to-point connection counter region indicates the number of point-to-point (p2p) connections existing in the output plug. A channel number region indicates a channel number which can be used for the output plug to transmit an isochronous data flow when the output plug is activated. A data rate region indicates a transmission speed (or bit rate) required for the output plug to transmit the isochronous packet of an isochronous data flow when the output plug is activated. An overhead ID region indicates the bandwidth required in addition to a bandwidth required for transmitting the payload of an isochronous packet. The payload region indicates the maximum size of isochronous data to be output from the output plug when the output plug is activated.
The format of the 32-bit iPCR 211 shown in FIG. 3 is as follows. The numbers below each region denote the number of allocated bits. An on-line region indicates whether the relevant input plug is on-line (“1” value) or off-line (“0” value). A broadcast connection counter region indicates whether a broadcast-in connection exists (“1” value) or not (“0” value) in the input plug. A point-to-point connection counter region indicates the number of p2p connections existing in the input plug. A channel number region indicates a channel number which can be used for the input plug to receive an isochronous data flow.
Accordingly, if a control device having a controller 300 is allocated a channel value to be used to write each channel value allocated in oPCR 111 and iPCR 211 in channel number shown in FIGS. 2 and 3 and to write other control values (i.e., on-line bit value, connection counter value, etc.) in the oPCR 111 and the iPCR 211, the respective source and sink devices transmit or terminate transmission of the information depending on those values.
As shown in FIGS. 2 and 3, there are two kinds of connections for transmitting information: the p2p connection and the broadcast connection. In the case of the p2p connection, only the control device which establishes a connection can terminate the connection. Thus, in the case where a third-party control device establishes a p2p connection between the source and sink, the source and sink device must each transmit and receive information even if the devices do not desire to do so.
To overcome the above problem, when either device does not desire to receive or transmit data any longer, an algorithm for informing a control device or the connected other device of this fact has been presented by defining a new control command in an audio-video/control command transaction set (AV/C CTS). Specifically, when any change occurs in a device for transmitting or receiving real time data, a new control command is defined in AV/C CTS to indicate this change. According to the AV/C CTS, information is available regarding whether each input plug desires to receive any input information, and whether each output plug desires to output information. Further, this is the case if a signal output from an output plug is transformed. However, when using a command of the AV/C CTS, there is a problem in that changes in other factors for controlling data flow, such as the bandwidth and information as to how many devices are connected to a particular connection, are not available.